The automatic stacking of units on a support, in particular a pallet or a rolling truck, with the packing units forming a stack, i.e. palletising, is known. However, such known palletising operations frequently use packing units of a uniform size or dimension and configuration which are typically lowered or placed or put down by robots, grabbers etc. in spaces determined by computer.
In contrast, the process of automatically loading a load carrier with packing units having different dimensions and configurations and materials, in order to form a stack, is known as automatic “mixed-case” palletising. In addition to having non-uniform dimensions, the packing units may also vary in configuration, i.e. they may include hard or soft packages, flexible packages, or packages having different shapes such as square, round or other non-uniform shapes etc.
In automatic mixed-case palletising, different aspects must be taken into consideration which drastically increase the complexity as compared to “simple” stacking, such as stacking packing units of uniform qualities as discussed above. For example, a subsequent packing unit can only be stacked or lowered or put down effectively onto a preceding packing unit if the preceding unit has a flat or planar upper surface, the two packing units are approximately horizontally aligned, and the preceding packing unit is able to support the weight of the subsequent packing unit placed upon it without being damaged.
The formed stack should also have a high degree of stability to promote, inter alia, a stack that is not prone to fall over during transportation. Although film wrapped around the stack does provide some assistance in this respect, it is generally insufficient to stabilise an otherwise incorrectly formed stack. A further consideration is that customers require, with increasing frequency, optimization of the stacks to facilitate a desired unloading sequence. Moreover, the wide diversity of physical characteristics among packing units combined with additional considerations such as those mentioned above have made it difficult to handle and/or grab such packing units automatically. Thus, packing units or goods of varying characteristics, such as different sizes and dimensions, are typically stacked by hand in light of stringent requirements for the stability of the stack, packing density within the stack, the sequence of loading and unloading, and the stacking-suitability of the goods. Further, known methods and devices have failed to meet these requirements.
Some previously known palletizing devices do not raise the packing units by means of a grabber, but rather displace them in one plane only. For example, devices for automatically loading a load carrier with packing units to form a load stack are known, such as the device of European Patent No. EP 1 462 394 B1. In such devices, the packing units are generally not lifted. For example, the packing units may be supplied seated on trays and lowered from the trays onto a packing table. The packing unit, whilst lying on the table, is displaced by a pusher along the broadside of a pallet waiting to be loaded, until the packing unit is moved to desired loading coordinates in an X-direction. Then, another pusher and a loading guide push or displace the packing unit over the pallet along the loading depth until the packing unit is moved to desired loading coordinates in a Z-direction. Then, the loading guide moves back, wherein the pusher remains stationary and serves as a stripper, so that the packing unit is set down on the pallet at the desired position. The resulting stack is supported by a loading aid on the remaining three sides. Stacking is thus performed quasi “against the wall”.
Such known devices and methods only allow access to a pallet or a rolling truck from one side. Thus, any respective packing unit can only lower to a certain extent into a free space within any given sequence of packing units within a stack. Moreover, after each loading procedure, the pallet is adjusted in height to load the next free space, if the pallet is loaded by the “mixed-case” method, discussed above. Further, it is time-consuming to displace articles on a packing table using pushers and, combined with the limited free space and restricted accessibility, this has drawbacks when forming the packing pattern. It has also been found that such a device cannot be used for stacking all existing types of packing units.
A grabber used for the purpose of raising and moving a plurality of different packing units in order to perform a stacking procedure is also known, an example of which is available from the company Ro-Ber Industrieroboter GmbH, Kamen. As shown in Logistik im Unternehmen [Business Logistics], book 4/5, vol. 13 (1999), pages 76 to 78, the Ro-Ber grabber includes a support comb on which a packing unit is received, and a hold-down device, such as for mechanically clamping the packing unit at the top and bottom to permit safe transportation or movement of the packing unit. Furthermore, the packing unit is additionally fixed or immobilized from the side by a vacuum or suction device. In order to lower or set down the packing units, the mobile support comb is moved back and the packing unit set down, wherein it lies against a stationary stripper. However, the surface formed by the Ro-Ber support comb does not change in size, allowing packing units which are larger than the surface to protrude beyond same. In the event of low intrinsic stability or defective packaging of the packing units this can cause parts of the packing units to dangle or even to be lost. Potentially, this could lead to a crash or to incomplete order processing.
The sequence and selection of packing units to occupy the free space in a stack produces a stack having the desired characteristics, such as stability and packing density. Further, it provides the ability to handle various different packing units for creating such a stack using a single “universal” grabber.